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The reduction in the cost of PV energy is still required to be competitive as an alternative energy source. The efficiency and reliability of PV inverters are important aspects to be enhanced to reduce the cost of PV energy since it is closely related not only to the annual energy production but also to the reduction of operational and maintenance costs of PV systems. In this paper, a single-phase IT-type NPC inverter with one-leg clamping pulse width modulation (OLC-PWM) is proposed for efficiency and reliability improvements. The proposed IT-type NPC inverter with OLC-PWM can improve the efficiency by taking the advantages of I-type and T-type NPC inverters regarding the power loss. Furthermore, its reliability has been improved compared with conventional I-type and T-type NPC inverters. The IT-type NPC inverter also has an ability to balance the neutral-point voltage. The superiorities of the proposed IT-type NPC inverter in terms of reliability and efficiency are validated through the simulations and experiments by comparing the reliabilities and efficiencies of the conventional I-type and T-type, asymmetric I-type and T-type and IT-type NPC inverters.

In the work reported in this paper, the converter-level lifetime evaluation of power devices in a railway propulsion inverter is performed to assess and compare operating strategies of a railway vehicle in terms of reliability. Two groups of velocity profiles are considered for the lifetime evaluation, wherein all the velocity profiles have the same running distance and time. The first group consists of three operation velocity profiles with the same acceleration at starting and stopping, but with different cruising ranges. In the second group, three operation velocity profiles with different coasting times and acceleration values are considered. A strategy to improve the lifetimes of power devices in propulsion inverters is proposed for vehicles on a busy railway line.

The long-term mission profile-based lifetime evaluation of a PV inverter plays an important role in the Design for Reliability approach to ensure the required reliability performance. In previous studies, different thermal loading definitions have been considered for the mission profile-based lifetime estimation of power devices. It may affect the reliability prediction result considerably but its impact has not yet been studied. In this paper, the effect of thermal loading definitions on the predicted reliability of power devices in a PV inverter is investigated. The thermal loadings and reliability of power devices of a single-phase five-level T-type inverter by considering four different thermal loading definitions are comparatively analyzed and further discussed. Finally, some guidelines for selecting the thermal loading definition are suggested.

Power electronics inverters are one of the major failure sources in motor drive systems, and power devices are one of the main causes of the power electronics inverter failures. Typically, an insulated-gate bipolar transistor (IGBT) module has multiple power devices due to some technical and cost advantages. This kind of configurations could have an asymmetric internal layout, which may lead to different thermal loadings and thereby lifetime difference of the power devices. Therefore, both the power rating and the lifetime of inverters are limited by the most stressed device. However, generally common data are provided for all devices in the datasheet and this may cause improper design of the inverters in terms of the lifetime and the power rating. In this paper, an effect of an asymmetric layout of IGBT modules on the reliability of motor drive inverters is studied based on a three-phase motor drive application with a 600 V, 30 A, three-phase transfer molded IGBT module. The thermal impedances of six IGBTs are investigated and its effect on thermal loadings of power devices is studied under the given mission profile. Then, their lifetimes are estimated and compared. Finally, this effect is verified by the experiments.

Due to the continuous demands for highly reliable and cost-effective power conversion, quantified reliability performances of the power electronics converter are becoming emerging needs. The existing reliability predictions for the power electronics converter mainly focus on the metrics of lifetime, accumulated damage, constant failure rate, or mean time to failure. Nevertheless, the time-varying and probability-distributed characteristics of the reliability are rarely involved. Moreover, in the public literatures, there are few evidences showing that the accuracy of the predicted reliability was experimentally validated. In this paper, a more advanced metric “cumulative distribution function (CDF)” is introduced to predict the reliability performance of the power electronics system based on mission profiles in motor drive application. Furthermore, the accuracy of the predicted reliability metrics is verified through a series of wear-out tests in a converter testing system. It is concluded that the CDF is a very suitable metric to predict the reliability performance of the converter, and it has shown good accuracy with much more reliability information compared to the existing approaches. In this method, the correct stress translation and dedicated strength tests based on mission profiles are two key factors to ensure the efficiency and accuracy of reliability prediction.

In this paper, an effect of junction temperature swings (ΔTj) on reliability of IGBT modules is studied with 600 V, 30 A, transfer molded power modules. This study is based on power cycling test results of 18 IGBT modules under three different junction temperature swings, namely 40 °C, 60 °C and 70 °C, by means of an advanced power cycler. The advanced power cycler allows performing power cycling tests under similar conditions of IGBT modules in power electronics applications. This paper presents post-failure analysis of the tested IGBT modules of interest in order to investigate the failure mechanism and also to compare results under different Tj. Further, a lifetime factor in respect to ΔTj is modeled with different lifetime definitions and confidence levels. This paper enables a better understanding of the junction temperature swing-related failure mechanisms and reliability performance of transfer molded IGBT modules for power electronics applications.

The complete percentile lifetime models are essentially required for a mission profile based reliability evaluation of power modules. However, the information on the complete lifetime models or lifetime data of power modules is rarely fully provided by manufacturers. The Monte Carlo method is a good solution to obtain the time-dependent reliability function when only limited lifetime information such as a certain Bx lifetime is given. However, there is a lack of research on the accuracy of the reliability function obtained by the Monte Carlo analysis. In this paper, a time-dependent reliability function of the IGBT module which is obtained by Monte Carlo method from a certain Bx lifetime is compared with that estimated by the complete percentile lifetime model in the case study of motor drive inverter. The complete percentile lifetime model is developed by the use of power cycling test results of 30 IGBT modules.

In this paper, the effect of the heat-pipe cooling system design processes on the reliability of the power module in a railway propulsion inverter was investigated. The existing design processes for the heat-pipe cooling system guarantee that the junction temperature of power devices does not exceed the maximum allowable junction temperature when the railway propulsion inverter operates under its mission profile; therefore, each step of the design process was reviewed to analyze the effect of the heat-pipe cooling system. Based on the processes, in the calculation for the required thermal resistance of the heat-pipe cooling system, two difference losses were considered with the thermal resistances of the insulated gate bipolar mode transistor (IGBT) module and the thermal grease at an interface between the baseplate of IGBT module and heat-pipe cooling system. The control scheme and mission profile of the train were taken into account to calculate the power losses. Then, the designed heat-pipe cooling systems were compared in terms of the size and weight. In addition, the junction temperatures and lifetimes of the power module with heat-pipe cooling systems designed by different power losses were estimated and compared. Finally, guidelines for a heat-pipe system cooling design are proposed.

Power electronic systems have gradually gained an important status in a wide range of industrial applications such as renewable generation, motor drives, automotive, and railway transportation. Accordingly, recent research makes an effort to improve the reliability of power electronic systems to comply with more stringent constraints on safety, cost, and availability. The power devices are one of the most reliability-critical components in power electronic systems. Therefore, its condition monitoring plays an important role to improve the reliability of power electronic systems. This paper proposes a condition monitoring method of insulated-gate bipolar transistor (IGBT) modules. In the first section of this paper, a structure of a conventional IGBT module and a related parameter for the condition monitoring are explained. Then, a proposed real-time on-state collector-emitter voltage measurement circuit and condition monitoring strategies under different operating conditions are described. Finally, experimental results confirm the feasibility and effectiveness of the proposed method.

This paper proposes the sinusoidal third harmonic voltage injection pulse-width modulation method for applying the LCL filter to Vienna rectifiers. The LCL filter can lead to the resonant problem in the CL part of LCL filter. This problem generates the current oscillation at the resonant frequency; therefore, the system using LCL filter becomes unstable. To overcome this problem, the controller bandwidth, switching frequency, PWM method, and active damping method are considered in design process. However, the existing PWM methods for the full power factor operation generates the resonant current. The proposed method injects the sinusoidal third harmonic voltage to the sinusoidal reference voltages. The magnitude and phase of the injection voltage are determined depending on the modulation index, power factor, filter impedances, and grid magnitude. Compared to other PWM methods, the probability of the resonant problem due to the PWM method is eliminated by using the proposed method. The effectiveness and performance of the proposed sinusoidal third harmonic voltage injection method are verified by simulation.

In multi-chip power modules, each power device could have different thermal impedance due to an asymmetric internal layout of the power module. This may lead to different thermal loadings and thereby having lifetime difference of the power devices in practical applications. Both lifetime and power rating of motor drives are limited by the most stressed device. Therefore, the reliability of motor drive can be improved by increasing the lifetime of the most stressed device. In this paper, the asymmetric Pulse Width Modulation (PWM) method to increase the reliability of inverters in motor drive systems has been proposed. The effect of an asymmetric layout of IGBT modules on the reliability of motor drives is studied based on a 3-phase motor drive application. Then, an asymmetric PWM method is proposed. Finally, the lifetime of the IGBT is compared before and after the proposed method is applied.

Wear-out condition monitoring of IGBT modules with failure mode separation gives some benefits. First, it allows proactive maintenance plans. Further, depending on the failure mode, different proactive control strategies can be applied to inverters in order to improve the reliability and availability of power electronic systems. This paper proposes a new method for the separation of two representative wear-out failure modes of wire-bonded IGBT modules in a grid-connected inverter in real time. The proposed method requires just two preliminary I – V characterizations of IGBT modules. Further, only one monitoring parameter is used, and thus, it is cost-effective compared with using one more monitoring parameter in order to separate failure modes. Experimental results verify the validity and feasibility of the proposed method.

One of the main purposes of an accelerated power cycling test is to develop a lifetime model for the lifetime prediction of power modules. It is important to select proper test conditions when the power cycling test is performed since it is closely related to the lifetime model parameters and also to the testing time. In this paper, the effects of power cycling test condition and test strategy on the lifetime estimation of power modules are studied. The lifetime models of the IGBT module are developed by the accelerated power cycling tests with different test conditions and also by calibrated accelerated power cycling test. As a case study, the lifetime of IGBT module in motor drive system is estimated with different lifetime models and the results are compared.

In this paper, the lifetime prediction of power device modules based on the linear damage accumulation is studied in conjunction with simple mission profiles of converters. Superimposed power cycling conditions, which are called simple mission profiles in this paper, are made based on a lifetime model in respect to junction temperature swing duration. This model has been built based on 39 power cycling test results of 600-V 30-A three-phase-molded IGBT modules. Six tests are performed under three superimposed power cycling conditions using an advanced power cycling test setup. The experimental results validate the lifetime prediction of the IGBT modules based on the linear damage accumulation by comparing the test results with the predicted lifetime from the lifetime model. Furthermore, the test results show the importance of the junction temperature swing duration effect for the lifetime prediction of IGBT modules under power converter applications.

Power cycling test is one of the important tasks to investigate the reliability performance of power device modules in respect to temperature stress. From this, it is able to predict the lifetime of a component in power converters. In this paper, representative power cycling test circuits, measurement circuits of wear-out failure indicators as well as measurement strategies for different power cycling test circuits are discussed in order to provide the current state of knowledge of this topic by organizing and evaluating current literature. In the first section of this paper, the structure of a conventional power device module and its related wear-out failure mechanisms with degradation indicators are discussed. Then, representative power cycling test circuits are introduced. Furthermore, on-state collector–emitter voltage $(V_{{\rm{CE\_ON}}})$ and forward voltage $(V_{F})$ measurement circuits for wear-out condition monitoring of power device modules during power cycling test are presented. Finally, different junction temperature measurement strategies for monitoring of solder joint degradation are explained.

An IGBT module has typically multiple power devices for some technical and cost advantages. This kind of configurations could have an asymmetric layout, which may lead to different thermal loadings and thereby lifetime difference of the power devices. Therefore, both the power rating and lifetime of inverters are limited by the most stressed devices. However, generally common data is provided for all devices and this may cause improper design of the inverters in terms of power rating and lifetime. In this paper, the effect of an asymmetric layout of IGBT modules on the reliability of power inverters is studied based on a 3-phase motor drive application with a 600 V 30 A, 3-phase transfer molded IGBT module. The thermal impedances of 6 IGBTs are investigated and its effect on the thermal loadings of power devices is studied under the given mission profile. Finally, their lifetimes are estimated and compared.

Due to the continuous demands for highly reliable and cost-effective power conversion, the quantified reliability performances of the power electronics converter are becoming emerging needs. The existing reliability modelling approaches for the power electronics converter mainly focuses on the predictions of lifetime, accumulated damage, constant failure rate or Mean-Time-To-Failure (MTTF), while the time-varying and probability-distributed characteristics of the reliability are rarely involved. In this paper, more complete metrics are introduced to quantify and characterize the reliability performance of power electronics system. The final predicted results showed good accuracy with much more reliability information compared to the existing approaches, and the quantified reliability correlation to the mission profiles of converter is mathematically established.

A major drawback of the NPC inverter is an unequal power loss distribution among the power devices which leads to unequal temperature stress among them. Therefore, certain power devices experience higher temperature stress, which is the main cause of power device module failure and thus both the power rating and lifetime of the NPC inverter are limited by the most stressed devices. In this paper, an asymmetric power device rating selection method for the NPC inverter is proposed in order to balance the lifetimes of the power devices. The thermal distribution of the power devices is analyzed based on 30 kW NPC inverter as a case study. Analytical power loss and thermal impedance models depending on the chip size are derived. Finally, using these models, the junction temperatures of the power devices depending on the chip size is discussed and a proper chip size for an even temperature distribution in the NPC inverter is selected.

This paper proposes an accurate method to estimate the junction temperature using the on-state collector-emitter voltage at high current. By means of the proposed method, the estimation error which comes from the different temperatures of the interconnection materials in the module is compensated. Finally, it leads to satisfactory estimated results. The proposed method has been verified by means of an IR (Infra-Red) camera during power converter operations when the loading current is sinusoidal.

Power electronics plays an important role in a wide range of applications in order to achieve high efficiency and performance. Increasing efforts are being made to improve the reliability of power electronics systems to ensure compliance with more stringent constraints on cost, safety, and availability in different applications. This paper presents an overview of the major failure mechanisms of IGBT modules and their handling methods in power converter systems improving reliability. The major failure mechanisms of IGBT modules are presented first, and methods for predicting lifetime and estimating the junction temperature of IGBT modules are then discussed. Subsequently, different methods for detecting open- and short-circuit faults are presented. Finally, fault-tolerant strategies for improving the reliability of power electronic systems under field operation are explained and compared in terms of performance and cost.

This paper proposes a method to reduce the low-frequency neutral-point voltage oscillations. The neutral-point voltage oscillations are considerably reduced by adding a time-offset to the three phase turn-on times. The proper time-offset is simply calculated considering the phase currents and dwell time of small and medium voltage vectors. The proposed method does not affect the outputs and there is no increase in the switching frequency. Further, it does not require additional hardware or complex calculations. Simulation and experimental results verify the validity and feasibility of the proposed strategy. This paper proposes a method to reduce the low-frequency neutral-point voltage oscillations. The neutral-point voltage oscillations are considerably reduced by adding a time-offset to the three phase turn-on times. The proper time-offset is simply calculated considering the phase currents and dwell time of small and medium voltage vectors. The proposed method does not affect the outputs and there is no increase in the switching frequency. Further, it does not require additional hardware or complex calculations. Simulation and experimental results verify the validity and feasibility of the proposed strategy.

In this paper, the effect of junction temperature swing duration on lifetime of transfer molded power insulated gate bipolar transistor (IGBT) modules is studied and a relevant lifetime factor is modeled. This study is based on 39 accelerated power cycling test results under six different conditions by an advanced power cycling test setup, which allows tested modules to be operated under more realistic electrical conditions during the power cycling test. The analysis of the test results and the temperature swing duration dependent lifetime factor under different definitions and confidence levels are presented. This study enables to include the t △ Tj effect on lifetime model of IGBT modules for its lifetime estimation and it may result in improved lifetime prediction of IGBT modules under given mission profiles of converters. A postfailure analysis of the tested IGBT modules is also performed.

In this paper, the lifetime prediction of power device modules based on the linear damage accumulation in conjunction with real mission profile assessment is studied. Four tests are performed under two superimposed power cycling conditions using an advanced power cycling test setup with 600 V, 30 A, 3-phase molded IGBT modules. The superimposed power cycling conditions are made based on a new lifetime model in respect to junction temperature swing duration, which has been developed based on 39 power cycling test results. The experimental results validate the lifetime prediction of the IGBT modules based on the linear damage accumulation by comparing it with the predicted lifetime from the lifetime model.

The thermal loading of power electronics devices is determined by many factors and has being a crucial design consideration because it is closely related to the reliability and cost of the converter system. In this paper the impacts of the ripple current to the loss and thermal loading, as well as reliability performances of power devices are comprehensively investigated and tested. It is concluded that the amplitude of ripple current may modify the loss and thermal loading of the power devices, especially under the conditions of converter with low power output, and thus the lifetime of devices could be disturbed.

Power cycling (PC) test is one of the important test methods to assess the reliability performance of power device modules related to packaging technology, in respect to temperature stress. In this paper, an advanced power cycler with a real-time V CE _ ON and V F measurement circuit for the IGBT and diode, which for the wear-out condition monitoring are presented. This advanced power cycler allows to perform power cycling test cost-effectively under conditions close to real power converter applications. In addition, an intelligent monitoring strategy for the separation of package-related wear-out failure mechanisms has been proposed. By means of the proposed method, the wear-out failure mechanisms of an IGBT module can be separated without any additional efforts during the power cycling tests. The validity and effectiveness of the proposed monitoring strategy are also verified by experiments.

This paper proposes a new modulation strategy that balances the neutral-point voltage for three-level neutral-clamped inverter systems. The proposed modulation replaces the P-type or N-type small switching states with other switching states that do not affect the neutral-point voltage. The zero and medium switching states are employed to help the neutral-point voltage balancing. This method little bit increases the switching events and output total harmonic distortion. However, this method has a strong balancing ability at all regions. Further, it is very simple to implement in both space vector modulation and carrier-based PWM methods. Simulation and experimental results verify the validity and feasibility of the proposed new modulation strategy.

This paper presents an open-circuit fault detection method for a grid-connected neutral-point clamped (NPC) inverter system. Further, a fault-tolerant control method under an open-circuit fault in clamping diodes is proposed. Under the grid-connected condition, it is impossible to identify the location of a faulty switch by the conventional methods which usually use the distortion of outputs because the distortion of the outputs is the same in some fault cases. The proposed fault detection method identifies the location of the faulty switch and the faulty clamping diode of the NPC inverter without any additional hardware or complex calculations. In the case of the clamping diode faults, the NPC inverter can transfer full rated power with sinusoidal currents by the proposed fault-tolerant control. The feasibility of the proposed fault detection and the fault-tolerant control methods for the grid-connected NPC inverter are verified by simulation and experimental results.

Molded IGBT modules are widely used in low power motor drive applications due to their advantage like compactness, low cost, and high reliability. Thermo-mechanical stress is generally the main cause of degradation of IGBT modules and thus much research has been performed to investigate the effect of temperature stresses on IGBT modules such as temperature swing and steady-state temperature. The temperature swing duration is also an important factor from a real application point of view, but there is a still lack of quantitative study. In this paper, the impact of temperature swing duration on the lifetime of 600 V, 30 A, 3-phase molded Intelligent Power Modules (IPM) and their failure mechanisms are investigated. The study is based on the accelerated power cycling test results of 36 samples under 6 different conditions and tests are performed under realistic electrical conditions by an advanced power cycling test setup. The results show that the temperature swing duration has a significant effect on the lifetime of IGBT modules. Longer temperature swing duration leads to the smaller number of cycles to failure. Further, it also shows that the bond-wire crack is the main failure mechanism of the tested IGBT modules.

In this paper, the effect of junction temperature swing duration on the lifetime of a transfer molded Intelligent Power IGBT Module is studied and a relevant lifetime factor is modeled. A temperature swing duration dependent lifetime factor is defined based on 38 accelerated power cycling test results under 6 different conditions and it may improve a lifetime model for lifetime prediction of IGBT modules under various mission profiles of converters. The power cycling tests are performed by an advanced power cycling test setup which enables tested modules to be operated under more realistic electrical conditions during the power cycling test. The analysis of the test results and the temperature swing duration dependent lifetime factor under different definitions and confidence levels are presented.

This paper presents a neutral-point voltage balancing method for three-level inverter systems using a time-offset estimation scheme. The neutral-point voltage is balanced by adding a time-offset to the turn-on time of the switches. If an inaccurate time-offset is added, the neutral-point deviation still remains. An accurate time-offset is obtained through the proposed time-offset estimation scheme. This method is implemented without additional hardware, complex calculations, or analysis. The effectiveness of the proposed method is verified by experiments.

Power electronic systems have gradually gained an important status in a wide range of industrial applications such as automotive, motor drives, railway transportation and renewable generation. Accordingly, recent research makes an effort to improve the reliability of power electronic systems to comply with more stringent constraints on safety, cost and availability. The power devices are the one of the most reliability-critical components in power electronic systems. Therefore, its condition monitoring plays an important role to improve the reliability of power electronic systems. This paper proposes a condition monitoring method of an IGBT module. In the first section of this paper, the structure of a conventional IGBT module and related parameter for the condition monitoring are explained. Then, an intelligent on-state collector-emitter voltage measurement circuit and condition monitoring strategies depending on converter operating conditions are described. Finally, experimental results confirm the feasibility and effectiveness of the proposed method.

This paper proposes a fault-detection method for an open-switch fault in the switches of grid-connected neutral-point-clamped inverter systems. The proposed method can not only detect the fault condition but also identify the location of the faulty switch. In the proposed method, which is designed by incorporating a simple switching control in the conventional method, the fault condition is detected on the basis of the radius of the Concordia current pattern, and the location of the faulty switch can be identified. By using the proposed method, it is possible to detect the open-switch fault and identify the faulty switch within two fundamental periods, without using additional sensors or performing complex calculations. Simulations and experiments are carried out to confirm the reliability of the proposed fault-detection method.

Multilevel rectifier topologies are commonly used in wide-power range applications. The T-type rectifier topology, which is a three-level topology, has an advantage in terms of efficiency compared to a neutral-point clamped (NPC)-type topology. In applications using the T-type rectifier topology, improving reliability has gained increased attention recently. A tolerance control for T-type rectifiers is necessary to improve the reliability of applications. When an open fault of switches connected to the neutral-point occurs, the NPC-type rectifier cannot restore distorted input currents, on the other hand, the T-type rectifier can eliminate the input current distortion completely. In this paper, we report two studies: 1) a three-level switching-oriented tolerance control, which is advantageous in terms of efficiency, for the Sx2 and Sx3 open-switch faults of the T-type rectifier and 2) comparison of the proposed tolerance control with two existing tolerance controls. In particular, the current total harmonic distortion, dc-link voltage ripple, and switch losses of these tolerance controls are analyzed by using simulation and experimental results.

This paper proposes a novel active T-type three-level converter concept with fault-tolerant control. With the proposed topology, the converter can be operated continuously under open-circuit faults. It is shown that the proposed topology not only can keep its outputs under open-circuit fault condition without degradation of performance but can also reduce the thermal stresses in neutral-point power devices by redundant current path. The junction temperature reduction in the neutral-point devices could improve the lifetime of the system under some operating conditions especially when the neutral-point devices have the highest thermal stresses. The feasibility and effectiveness of the proposed topology concept are verified by the simulation results.

The centralized topology with three-level inverters are widely used in photovoltaic (PV) systems due to their less installation costs and complexity. However, the common maximum power point tracking (MPPT) is a disadvantage of the centralized topology particularly under the partial shading and panel mismatch conditions. In this system, if PV modules are separately connected to the split capacitor voltage, the MPPT efficiency can be improved by the proposed control strategy. By the proposed method, the two capacitor voltages can be controlled asymmetrically to perform the separate MPPTs of each PV module connected to separate capacitors. The outputs can be generated without distortion even if two capacitors are asymmetrically regulated. Simulation and experimental results verify the validity and feasibility of the proposed methods.